As disclosed in March, Advanced Organic Chemistry, Second Edition, McGraw-Hill, New York, 1977, pp. 501-502; Olah, Friedel-Crafts and Related Reactions, Volume 2, Interscience Publishers, New York, 1963-1964, pp. 659-784; U. S. Pat. No. 2,516,971 (Galitzenstein et al.); and the references cited therein, it is known that aromatic compounds can be haloalkylated by reacting them with a hydrogen halide and an appropriate aldehyde in the presence of a Lewis acid or a proton acid as a catalyst, most commonly in the presence of zinc chloride.
The chloroalkylations utilizing formaldehyde as the aldehyde have been successfully employed in providing fairly high yields of 1-chloro-1-arylalkanes; reasonably high yields of 1-chloro-1-arylalkanes have also been obtained from chloroalkylations utilizing higher aldehydes in some cases, e.g., when the aromatic compound has had an appropriate functional substituent or a plurality of alkyl substituents; and reasonably acceptable, although lower, yields of 1-halo-1-arylalkanes have been obtained in comparable bromoalkylation reactions. However, when the aromatic compound has been a less reactive compound, e.g., an unsubstituted aromatic hydrocarbon or a monoalkylaromatic hydrocarbon, it has not been found possible to provide commercially acceptable yields of 1-halo-1-arylalkane, even when the haloalkylation has been a chloroalkylation rather than a bromoalkylation. There has been too much co-formation of diarylalkane by-product, especially in the bromoalkylation reactions.
Another disadvantage of the known haloalkylation processes utilizing the higher aldehydes has been their providing too much o-isomer in processes performed to provide 1-halo-1(4-alkylphenyl)alkanes, such as the compounds which have been synthesized by other techniques to provide intermediates for ibuprofen, related pharmaceuticals, detergents, etc. It would be desirable to find a way of increasing the para/ortho ratio obtainable from such processes to provide a more economical method of preparing the 1-halo-1-(4-alkylphenyl)alkanes which can be used in known processes, such as those of U. S. Pat. No. 4,536,595 (Gardano et al.), Canadian Patent No. 1,197,254 (Francalanci et al.), British Patent No. 1,560,082 (Dynamit Nobel), Czechoslovakian Certificate of Authorship 219,752 (Palecek et al.), and Japanese Kokai 47-39050 (Miyatake et al.) and 52-111536 (Tokutake).